1. Field of the Invention
This invention relates to a process for obtaining foodstuffs and/or beverages of various kinds, for instance coffee with milk, hygenically sealed in containers of various kinds, for instance cans.
2. Description of the Prior Art
Generally in filling food and/or drink in containers such as cans, for example, it is conventionally quite common to fill the food and/or drink in the container in the hot state, sometimes by reason of the preceding and/or subsequent processing steps and sometimes with the aim of attaining the pasteurizing effect, though of preliminary nature. It is conventional to perform the filling in continuous operation and, upon accumulation of a suitable number of the filled and sealed containers, to charge the containers into a pressure tank of considerably large volume for pasteurization or sterilization under heat in a batch manner. Therefore, the containers filled with the hot food and/or drink in a continuous operation must wait for some irregular length of time, until accumulation of the suitable number of them, before undergoing the pasteurization or sterilization treatment. Conventionally, the containers are left for said time intervals in ambient air without any particular processing, thus undergoing natural cooling. Duration of such natural cooling time is, as has already been referred to as "irregular time", differs from one container to another, according to whether they have been filled and sealed earlier or later, since the filling and sealing of the containers are in the continuous operation and the pasteurization or sterilization is in the batch operation. When charged into the pressure tank, the temperature is therefore different from one container to another. Starting from such different initial conditions, the containers undergo diverse heating or temperature increases in the pressure tank. Duration of the heat treatment time after heated to the effective pasteurizing temperature is thus diverse from one container to another. The taste of some food or drink is quite sensitive to the cooling condition and to the temperature and duration of the pasteurization or sterilization treatment, and thus the irregularities of the heat-treatment condition as mentioned above have resulted in the disadvantage of failure to guarantee a constancy in taste of the sealed food and/or drink from one container to another. This disadvantage is quite detrimental, particularly when the sealed drink is coffee, one of the most important features of which is the aroma.
As a remedy for the above disadvantages, it might be considered to work out an overall continuous operation system where the containers are first continuously filled and sealed and then without interrupting stacking or storing they are serially subjected to the subsequent pasteurizing or sterilizing process as the latter part of a continuous operation. However, such a system is, in fact, hardly feasible in view of the technical difficulties and large installation costs, as may be understood from the explanation given hereunder.
Pasteurizing or sterilizing tanks can not be used to heat the containers under normal atmospheric pressure since the inner pressure of the heated containers may be high enough to deform or burst the containers if treated in such open air condition. By way of practical example, coffee cans made of aluminum with an easy open end as commonly used these days may sometimes deform and burst out when heated to 120.degree. C in open air condition, even though the inner pressure was subatmospheric at normal room temperature, say somewhat below 300 mm Hg at 20.degree. C. Therefore, in order to safely raise the temperature of these cans for pasteurization or sterilization, it is required to keep the inner space of the treating tank under raised pressure conditions in response to the increase in the temperature of the cans. However, it is technically difficult and will result in big installation costs to maintain the tank chamber at high pressure while admitting smoothly continuous charging of the filled and sealed containers into the chamber.